We plan to continue our study of the synthesis and turnover of small intestine proteins. Special attention will be paid to the role of intraluminal factors (bacterial glycosidases and pancreatic proteases) on the structure and function of intestinal proteins and to their role in enhancing protein turnover on the brush border membrane. We also plan to purify three specific proteins in order to study their function and mechanism of action - i.e., alkaline phosphatase, IF-B12 receptor, and calcium binding protein. We will examine the role of phosphate transport in relationship to alkaline phosphatase activity, the fate of IF and B12 during absorption, and the relationship of calcium binding protein to calcium absorption. Three experimental models new to our research will be extensively used to look at some of these problems: the postnatal development of the rat small intestine, mice with exocrine pancreatic insufficiency, and the isolated perfused small intestine. Work on each of these models has already begun. The remaining methods have been previously employed by us - protein purification, analysis of carbohydrate content, polyacrylamide electrophoresis, brush border isolation and radioisotope incorporation into macromolecules. Where possible, the relevance to clinical disease will be examined. For example, bacterial overgrowth syndromes may be associated with enhanced glycosidase action on the membranes, pancreatic insufficiency leads to B12 malabsorption, and calcium binding protein may be abnormal in malabsorption states or uremia. Each of these conditions will be examined with the appropriate assay.